1. Field of the Invention
The present invention relates to an optical cross-connect device in an optical transmission system, and, more particularly, to a bit-rate-independent optical cross-connect device.
2. Description of the Related Art
A light transmission system can adopt various protocols, such as FDDI (Fiber Distributed Data Interface), ESCON (Enterprise Systems Connectivity), Fiber Channel, Gigabit Ethernet, and ATM (Asynchronous Transfer Mode) for high-bandwidth and high-bit-rate bit-rate communications. Fiber optics technology can adopt various bit rates of 125 Mb/s, 155 Mb/s, 200 Mb/s, 622 Mb/s, 1062 Mb/s, 1.25 Gb/s, and 2.5 Gb/s to supply the capacity to meet the demand for multimedia applications.
In operation, the light transmission system adopts one set of protocols as a multiplexing format for using any number of bit rates. In this type of light transmission system, the bit rate of an optical signal is set previously to a specific rate, such that an optical receiver can be designed to match the incoming bit rate. The function of an optical receiver is to convert an input optical signal into an electric signal and thereafter restore the electric signal to the original data that is noise-free.
FIG. 1 is a block diagram illustrating a conventional optical cross-connect device using an electrical switch in an optical transmission system. As shown in FIG. 1, the optical transmission system includes: a demultiplexer (DMUX) 106 for demultiplexing an input optical signal into optical signals of different channels; a plurality of fixed bit-rate optoelectric converters 102 for converting the respective optical signal channel outputted from the demultiplexer 106 into electrical signals; and, an N×N optical cross-connect switch 103 for receiving the electrical signals outputted from the opto electric converters 102 and routing the received electrical signals to the intended path. The optical cross-connect device also includes a plurality of bit-rate-fixed electro-optic converter 104 for converting the electrical signals that are outputted from the respective output port of the optical cross-connect switch 103 into optical signals, and a multiplexer 107 for multiplexing the optical signals outputted from the bit-rate-fixed electro-optic converter 104 via a single optical fiber. The optical cross-connect switch 103 is connected to a controller 108 for controlling the input and output of data therefrom.
Now, the operation of the conventional optical cross-connect device with the above-mentioned configuration will be described.
The input optical signal is first applied to the demultiplexer 106, which demultiplexes the optical signal into different wavelengths. The optical signals outputted from the demultiplexer 106 are applied to the input terminals of the optoelectric converters 102, each supporting only a specific fixed bit rate. Thus, inputting an optical signal to each bit-rate-fixed optoelectric converter 102 is always performed at a fixed bit rate. The electrical signals outputted from the optoelectric converters 102 are applied to the input terminals of the N×N cross-connect switch 103. These electrical signals are then sent to the input terminals of the respective electrooptic converter 104, each supporting only a fixed bit rate. The electrical signal is inputted to each electro-optic converter 104 at a fixed bit rate. Thereafter, the electrical signals are converted into optical signals via the electro-optic converters 104, then outputted as an output optical signal after multiplexed by the multiplexer 107. Finally, the multiplexed optical signals are transferred via a single optical fiber.
The conventional optical cross-connect device, as described in the preceding paragraph, has a problem in that a desired connection for data transfer is allowed only for a particular transfer format as the optical cross-connect device is internally equipped with fixed bit-rate optoelectric converters (or optical receivers) and fixed bit-rate electro-optic converters (or optical transmitters). That is, the conventional optical cross-connect device has no ability, known as “transparency,” to cope with change in the transfer format or any variation in the bit rate. Hence, the conventional optical cross-connect device provides only a limited cross-connection in a fixed data network. As a result, there are problems associated with the multi-transfer requirements and the network management.
Another conventional optical cross-connect device is disclosed in Korean Patent Application No. 2000-28076 (Self-Healing Bit Rate Converting Device in Optical Transmission System) filed under the name of the assignee of the present invention. The Korean application provides a means to handle different bit rates in an optical receiver. In addition, the disclosed optical cross-connect device has a configuration, which includes a bit rate discriminating unit and a temperature sensing unit for each BICDR (Bit Rate Independent Clock and Data Recovery). As the performance of the BICDR transmitters and receivers are affected when operating at a considerably high temperature, the bit rate discriminating unit and the temperature sensing unit are operatively coupled to a central control unit to compensate for the temperature variation. However, the temperature of the BICDR transmitters and receivers may be different from one another. For this reason, it is necessary to control the respective bit rate discriminating unit of the BICDR transmitters and receivers in an independent fashion when determining the bit rate. Therefore, the present invention provides an improved optical cross-connect device capable of processing different bit rates without being affected by temperature variation.